This page is no longer in use: please go to the separate AwaP or IC plugin page.
AwaP-IC is a QGIS tool that calculates the Area-weighted average Perimeter (AwaP) and Interface Catchment (IC), two measures developed by Pafka & Dovey (2017), that combined, capture the capacities of urban morphologies to enable and attract pedestrian movement.
AwaP is a measure of urban permeability, that calculates the average perimeter of urban blocks within a study area, weighing the perimeter of each block by its area. This way the impact of a large block will be proportional with the share of the study area it occupies, and its effect as a major-barrier to movement is not lost in the average. The lower the AwaP, the easier is to walk through the urban fabric. An AwaP of 400m corresponds to a square block of 100x100m, often taken as the maximum block-length that still allows good permeability.
IC calculates the total length of public/private interfaces reachable from a starting point and within a given walking distance. IC is relevant for walking as most urban attractions, such as dwellings, shops and workplaces, are accessed through the public/private interface, where buildings meet the street. High IC values indicate high capacity for accommodating urban attractions. Together, these two measures account for both street width and block size, measuring both walkable access and what one gets access to.
While AwaP and IC should be considered together in the analysis of walkable access, in this 1.0 version of the AwaP-IC software the two measures are provided by distinct plugins. We plan to develp these plugins further for urban mapping, and join them into one tool.
The base requirement for the calculation of these measures is a layer of urban blocks drawn as polygons, or closed polylines. Lines within the blocks, such as lot subdivisions, will be ignored. However other errors in the urban blocks layer may not be recognised by the software, and may lead to errors, or long processing times. As both AwaP and IC are calculated in metres, a projected coordinate system should be used in the QGIS project. Instead of the very common WGS84 - EPSG:4326 which uses degrees as a unit for distance, the projected WGS84/Pseudo-Mercator - EPSG:3857 which measures distances in metres may be used.
It takes in several parameters in order to calculate AwaP:
Figure 1: AwaP plugin interface
Whether the blocks which are partly inside and partly outside of the area of interest should be considered in this calculation, would depend on the specifics of each research. The tool provides three options:
Figure 2: Examples of the urban blocks included in the AwaP calculation (dark red) when using different settings for blocks intersecting the study area boundary (black line).
Interface catchment (IC) is a measure of the total length of public-private interfaces within a given walking distance (Pafka and Dovey 2017). The difference between IC and other catchment metrics is that it also accounts for the street width. IC looks at which edges of urban blocks may be accessed from a given starting point within a maximum walking distance. The assumption here is that a person is able to walk through any open space that is not occupied by urban blocks.
The IC tool requires the following parameters to be set (Figure 3):
Starting point - A starting point from which the IC calculation will commence is required. This starting point can be set in one of three ways:
Regardless of which option has been used for selecting the starting point, when the plugin is run, the current coordinates present in these fields will be used to define the starting point for IC calculation.
Figure 3: IC plugin intefrace
Pafka E & Dovey K. (2017) Permeability and Interface Catchment: Measuring and Mapping Walkable Access. Journal of Urbanism 10(2): 150-162.
The development of this software has been supported by a seed grant provided by the Transport, Health and Urban Design (THUD) Research Hub of the Melbourne School of Design.